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Absolute Risk Reduction Formula:
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Absolute Risk Reduction (ARR) is the difference in event rates between control and experimental groups in clinical trials. It represents the absolute difference in risk of an outcome between two groups.
The calculator uses the ARR formula:
Where:
Explanation: ARR measures the actual reduction in risk attributable to the intervention, expressed as an absolute difference.
Details: ARR is crucial for understanding the clinical significance of treatment effects, calculating Number Needed to Treat (NNT), and making informed clinical decisions about therapeutic interventions.
Tips: Enter both CER and EER as proportions (values between 0 and 1). For example, 0.15 represents 15% event rate. CER should be the control group event rate and EER the experimental group event rate.
Q1: What is the difference between ARR and RRR?
A: ARR is the absolute difference in event rates, while RRR (Relative Risk Reduction) is the proportional reduction relative to the control group rate.
Q2: How is ARR related to NNT?
A: Number Needed to Treat (NNT) is calculated as 1/ARR. It represents the number of patients needed to treat to prevent one additional adverse outcome.
Q3: What does a negative ARR indicate?
A: A negative ARR suggests the experimental treatment may be harmful, as the event rate is higher in the experimental group than in the control group.
Q4: When is ARR more useful than RRR?
A: ARR is generally more clinically meaningful as it provides the actual magnitude of benefit, while RRR can be misleading when baseline risks are low.
Q5: What are typical ARR values in clinical trials?
A: ARR values vary widely by condition and intervention. Values of 0.01-0.10 are common, with higher values indicating more effective treatments.